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MAX9744 produce strange high voltage waveform
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MAX9744 produce strange high voltage waveform

by ehsanmasoumi on Sun Aug 30, 2020 4:10 am

Hi,
I assembled the MAX9744 as shown in the guide and connected it to Arduino. Because I want to use it in a circuit with pure resistive load, I connected a 12 ohms resistor to the right channel out put. Also, I used a power generator to send a sinusoidal waveform of 10Hz and 0.4mVpp into the right input channel. However, as soon as I connect the 12V supply to the board, it produce 100V and make the resistor so hot that it melts the solder less board. Whoever command I send through Arduino serial port also is not working. Can you please help me with this?

Attached is the picture of my wiring
Untitled.jpg
Circuitory
Untitled.jpg (713.79 KiB) Viewed 34 times

ehsanmasoumi
 
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Re: MAX9744 produce strange high voltage waveform

by adafruit_support_bill on Sun Aug 30, 2020 9:41 am

However, as soon as I connect the 12V supply to the board, it produce 100V and make the resistor so hot that it melts the solder less board.

How are you measuring that? The board does not have any voltage boosting capability. And 100v into a 12 ohm load would be more than 80 watts. That 1/4 watt resistor would probably not last more than a second or two.

Because I want to use it in a circuit with pure resistive load,

This amplifier is designed to drive inductive loads like speakers. Since it is a class D amplifier, the output is a high-frequency switched PWM.
https://learn.adafruit.com/adafruit-20w ... -2567778-9

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Re: MAX9744 produce strange high voltage waveform

by ehsanmasoumi on Sun Aug 30, 2020 5:23 pm

Thanks for quick response. I figured out that the probe setting of my oscilloscope was wrong. Now it is corrected and the voltage reading is correct. I tested it with some other sources.
The output voltage now dropped to 12 volts but I have few problems.
1- The output is not even close to the input.
2- The Arduino command is not working even when I type + or -. I also changed the volume to 10 in code.
Can you please help me to resolve this ?
Generator.jpg
Generator.jpg (971.79 KiB) Viewed 24 times

oscope.jpg
oscope.jpg (914.97 KiB) Viewed 24 times

wiring.jpg
wiring.jpg (815.75 KiB) Viewed 24 times

ehsanmasoumi
 
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Re: MAX9744 produce strange high voltage waveform

by ehsanmasoumi on Sun Aug 30, 2020 5:24 pm

also here is the supply I used to power the amp and the error I see
supply.jpg
supply.jpg (629.54 KiB) Viewed 24 times

window.jpg
window.jpg (839.51 KiB) Viewed 24 times

ehsanmasoumi
 
Posts: 4
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Re: MAX9744 produce strange high voltage waveform

by adafruit_support_bill on Mon Aug 31, 2020 5:53 am

1- The output is not even close to the input.

It will not be if driving a resistive load. This is a class D amplifier designed for driving inductive speaker-loads. The output of a class-D amp is high frequency PWM that requires filtering. This particular amp depends on the inductance of the speaker coil to filter out the class-D switching frequency.

2- The Arduino command is not working even when I type + or -. I also changed the volume to 10 in code.
Can you please help me to resolve this ?

Please post some close up photos showing your soldering.

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Re: MAX9744 produce strange high voltage waveform

by ehsanmasoumi on Mon Aug 31, 2020 1:33 pm

Thanks a lot. Here is the picture of my soldering
So should I put a resistive load before my resistor to fix the issue?

Thanks
Untitled.jpg
Untitled.jpg (921.81 KiB) Viewed 12 times

ehsanmasoumi
 
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Re: MAX9744 produce strange high voltage waveform

by adafruit_support_bill on Mon Aug 31, 2020 1:56 pm

Adding an inductor in series with your resistor should give you a cleaner waveform.

Your solder joints have not flowed onto the solder pads, so electrical connection will not be reliable. See this guide for some tips on identifying and repairing common soldering problems.

https://learn.adafruit.com/adafruit-gui ... n-problems

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